Formation of Intramolecular Poly(4-hydroxystyrene) Dimer Radical Cation

Abstract

Poly(4-hydroxystyrene) (PHS) has been used in lithography as a backbone polymer and is also a promising material for extreme-ultraviolet or electron beam lithography. The dynamics of PHS radical cations generated upon exposure to electron beam were investigated. The transient absorption of PHS was observed in the near-infrared region in p-dioxane solutions by pulse radiolysis. Charge resonance (CR) bands that represent pi-pi interaction between the two chromophores of the intramolecular PHS dimer radical cation were observed, whereas p-cresol shows no distinct CR band. Although the radical cations of phenol derivatives are known to be easily deprotonated, it was found that the dimer radical cation formation leads to less deprotonation by its charge resonance stabilization.

Radiation Chemistry in Chemically Amplified Resists

“…114) Hydroxyl groups are also important for proton generation from radical cations of alicyclic hydro- carbon polymers, which has been proved by comparing the polymer structure dependence of resist sensitivities to DUV, EB, and EUV. 154) Although the transient absorption spectra of the reactive intermediates of an aromatic polymer with hydroxyl groups such as PHS had not been reported until our studies, 152,155,156) the radiation chemistry of phenol derivatives has been well studied. Phenoxy radicals, which are stable decomposition intermediates of phenols, were first observed in the 1950s.…”

Secondary Electrons in EUV Lithography

“…(2) Ionization occurs when the free electron causes a bound electron to leave the molecule thereby creating a secondary electron and a hole. The original electron loses energy equivalent to the binding energy (6)(7)(8)(9)(10)(11)(12)(13)(14) large enough for this daughter electron to cause further ionization events. Conversely, in the process of photoionization, the incident photon transfers all of its energy to the photoelectron and then ceases to exist.…”

“…However, the details surrounding the chemical events leading to acid generation are still a matter of speculation, and while our group [6] and the groups of Kozawa and Tagawa [7][8][9][10] have attempted to examine this mechanism with various theoretical and experimental approaches, the details of these chemical events remain poorly understood.…”

Dynamics of radical cations of poly(4-hydroxystyrene) in the presence and absence of triphenylsulfonium triflate as determined by pulse radiolysis of its highly concentrated solution

“…Previous studies have determined the primary process after ionization of PHS by using pulse radiolysis [11][12][13][14][15][16]. These studies mainly used samples of diluted PHS solutions.…”

“…Pulse radiolysis, a time-resolved spectroscopic method used for ionized resist polymers such as novolaks [6,7], acrylates [8][9][10], and polyoxystyrenes [11][12][13][14][15][16], has been used to model base polymers of CARs. Pulse radiolysis studies of resist polymers have been conducted mainly in dilute solution.…”